Not knowing the full details of your application, my suggestion is that you might want to take a look at doing some additional delays of the automation to let your application catch up. Each time through the driver, if you're selecting "ClickItem", it's selecting an item but there's other processing going one where you're entering in data, clicking OK buttons, etc. It's entirely possible that when you get to the second time through the loop, there's enough going on behind the scenes that the combo box is not getting populated in time.
I see you're using aqUtils.Delay to put in some hardcoded delays. These may not be long enough to handle your specific situation. Instead of using aqUtils.delay, you might want to try something like this.
var replacesitem=Aliases.IEXPLORE.pageModuledetails.panelMsDlgcontent.panelMsDlgborder.panelMsDlgframecontainer.frameDlgframe8c026eae13514a938be.formAspnetform.panelS4Workspace.panelS4Bodycontainer.panelS4Mainarea.panelMsoContenttable.panelS4Ba.panelMsBodyareacell.Replaces;
while (replacesitem.WaitProperty("wItemCount", 0, 1000))
{
Delay(1000)
}
var listcount = replacesitem.wItemCount;
This is a rather "quick and dirty" insertion here and I'd recommend adding some code to break out of that new while loop if it takes too long. But the bolded code above will continue to loop so long as the item count in your combo box is zero. As soon as it becomes non-zero, you break out of the loop and continue in your code.
